For single player, even though I've never played Quake 2, I'd definantly have to go with Quake 1. For multiplayer I'd have to go with Quake Live, purly because I wasn't around when everyone was playing Quake 3 sadly :/

Oh,I'm sure ragers will show up to tear me to pieces.I'm pretty thick skinned,so what do I care?And anyway,we're ALL entitled to our own opinions,correct?
Anyway,DOOM still remains my favorite game of all time.

Quake 1's theme never really worked for me. I'm not a fan of gothic castles and dungeons. If they had done more tech levels I might have enjoyed it more.

I liked Quake 2 a lot more, despite some technical flaws. With its hub-based approach and alien tech base theme it featured my favorite elements of older games I liked.

Quake 3 is a tech demo, not a game. Without a decent single player campaign it fell flat on its face for me.

Quake 4 is just another modern alien Sci-Fi shooter with all the negatives implied by this description. The ultra-linear level design made the game an extreme snoozefest and I quit when I couldn't complete one of the vehicle missions due to an engine bug that caused me to die each and every time and had no chance anymore to restore to a point before that. This was also the last commercial game I ever played.

With all this talk of Quake II, I'm just wondering how many here actually still play online. There are usually at least a few well populated servers on the go at any time on master.q2servers.com. And with Q2Pro's built-in server browser (pic), finding a game is easier than ever (just make sure to set r_override_textures to 0 if you want the classic look).

If you're looking for a more vanilla experience, there are some other great ports out there, and servers that support the old .EXE. Just point the Quake II Server Browser (pic) to the .EXE, or your port of choice and get playing!